As the trend to inhibiting the release of carbon dioxide and depletion of oil resources has been rising, much is expected of the development of small vehicles using only electric power (for example, secondary batteries such as lead storage batteries) as drive power.
Among such power sources, lead storage batteries, which excel in toughness and have a suitable weight, can be considered useful as power sources, for example, in transport vehicles.
Various methods for accurately estimating the usage limit of lead storage batteries and rationally replacing the batteries have been studied. For example, Patent Document 1 describes a method by which a surface temperature of a lead storage battery using a trickle or a float (a lead storage battery that is trickle charged or float charged) is continuously measured and a capacity deterioration rate of the lead storage battery is calculated with consideration for the surface temperature. Patent Document 1 also describes an uninterruptible power source device that constantly supplies a very small charging current to the lead storage battery, wherein the capacity deterioration rate can be calculated with good accuracy with consideration for the dependence on the lead storage battery temperature. By using this method it is possible to estimate with good accuracy the usage limit of lead storage batteries that are used for various applications, and the effect obtained seems to be high.
The uninterruptible power source device described in Patent Document 1 is provided for use in case of power outage that occurs on an irregular base and normally is not discharged. However, the aforementioned transport vehicles normally consume power (travel). Moreover, in the transport vehicles, a rather remarkable SOC (State of Charge) of lead storage batteries is changed due to repeated travel (discharging) and charging. In such applications, the service life of the lead storage battery cannot be accurately estimated by simply measuring the surface temperature of the lead storage battery. Further, taking into account that the travel distance (SOC change) of a transport vehicle is not constant, and the input capacity (input electric quantity) per one cycle also varies, it appears to be difficult to estimate the service life of a lead storage battery by the number of charging cycles (number of cycles).
Patent Document 1: Japanese Patent Application Laid-Open No. 05-315015.